# ---
# title: 1394. Find Lucky Integer in an Array
# id: problem1394
# author: Tian Jun
# date: 2020-10-31
# difficulty: Easy
# categories: Array
# link: <https://leetcode.com/problems/find-lucky-integer-in-an-array/description/>
# hidden: true
# ---
# 
# Given an array of integers `arr`, a lucky integer is an integer which has a
# frequency in the array equal to its value.
# 
# Return _a lucky integer_  in the array. If there are multiple lucky integers
# return the **largest** of them. If there is no lucky integer return **-1**.
# 
# 
# 
# **Example 1:**
# 
#     
#     
#     Input: arr = [2,2,3,4]
#     Output: 2
#     Explanation: The only lucky number in the array is 2 because frequency[2] == 2.
#     
# 
# **Example 2:**
# 
#     
#     
#     Input: arr = [1,2,2,3,3,3]
#     Output: 3
#     Explanation: 1, 2 and 3 are all lucky numbers, return the largest of them.
#     
# 
# **Example 3:**
# 
#     
#     
#     Input: arr = [2,2,2,3,3]
#     Output: -1
#     Explanation: There are no lucky numbers in the array.
#     
# 
# **Example 4:**
# 
#     
#     
#     Input: arr = [5]
#     Output: -1
#     
# 
# **Example 5:**
# 
#     
#     
#     Input: arr = [7,7,7,7,7,7,7]
#     Output: 7
#     
# 
# 
# 
# **Constraints:**
# 
#   * `1 <= arr.length <= 500`
#   * `1 <= arr[i] <= 500`
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
